This project is concerned with studies of Rocky Mountain spotted fever and other tick-borne rickettsial diseases in the United States and in other countries regarding ecology, identification, and characterization of the reckettsial agent(s) with their associated vectors. With collaboration of outside agencies (state health departments, public health laboratories, hospitals, physicians, etc.) source material for comparative studies on the various rickettsial types and information about the distribution of vector species associated with spotted fever in the United States is obtained. This project also considers the cellular and subcellular aspects of interaction between tick-borne agents, particularly rickettsiae, and their vectors.